On 4/15/24 8:49 AM, Jianfeng Wang wrote:
> Added internal options for ftrace, and included a fgraph:retval
> option that will print the function names at the function exit.
> When the option is set and the function_graph retval feature is
> supported by the kernel, each function's return value will be
> printed as '(ret=retval)'.
>
> Signed-off-by: Jianfeng Wang <jianfeng.w.wang@xxxxxxxxxx>
> ---
> lib/trace-cmd/trace-ftrace.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/lib/trace-cmd/trace-ftrace.c b/lib/trace-cmd/trace-ftrace.c
> index cb05d88c..fecc3d69 100644
> --- a/lib/trace-cmd/trace-ftrace.c
> +++ b/lib/trace-cmd/trace-ftrace.c
> @@ -23,6 +23,12 @@ struct tep_plugin_option trace_ftrace_options[] = {
> .description =
> "Show the depth of each entry",
> },
> + {
> + .name = "retval",
> + .plugin_alias = "fgraph",
> + .description =
> + "Print function retval at function exit in function graph",
> + },
> {
> .name = NULL,
> }
> @@ -30,6 +36,7 @@ struct tep_plugin_option trace_ftrace_options[] = {
>
> static struct tep_plugin_option *fgraph_tail = &trace_ftrace_options[0];
> static struct tep_plugin_option *fgraph_depth = &trace_ftrace_options[1];
> +static struct tep_plugin_option *fgraph_retval = &trace_ftrace_options[2];
>
> static int find_ret_event(struct tracecmd_ftrace *finfo, struct tep_handle *pevent)
> {
> @@ -232,7 +239,7 @@ print_graph_entry_leaf(struct trace_seq *s,
> ret = trace_seq_printf(s, " (%lld)", depth);
>
> /* Return Value */
> - if (ret && fgraph_retval_supported)
> + if (ret && fgraph_retval->set && fgraph_retval_supported)
> ret = trace_seq_printf(s, " (ret=%lld)", retval);
>
> return ret;
> @@ -378,7 +385,7 @@ fgraph_ret_handler(struct trace_seq *s, struct tep_record *record,
> trace_seq_printf(s, " (%lld)", depth);
>
> /* Return Value */
> - if (fgraph_retval_supported)
> + if (fgraph_retval->set && fgraph_retval_supported)
> trace_seq_printf(s, " (ret=%lld)", retval);
>
> return 0;
Kindly ask for reviews on this patchset :)
Here, I include a more detailed effect of this patchset.
* Record process
The trace-cmd record process is not changed.
# trace-cmd record -p function_graph -P 4331
trace-cmd can communicate with the kernel to get the actual funcgraph_exit
event format. If the kernel supports ftrace-retval, then trace-cmd will
use the updated event format that has "retval" field.
* Report process
By default, trace-cmd won't print each function's retval.
# trace-cmd report
However, if one wants to turn it on and the kernel supports the feature,
do the following (through fgraph plugin options):
# trace-cmd report -O fgraph:depth -O fgraph:tailprint -O fgraph:retval
The output looks like this:
<idle>-0 [012] d.... 361.071503: funcgraph_entry: | switch_mm_irqs_off() { (0)
<idle>-0 [012] d.... 361.071507: funcgraph_entry: 0.491 us | load_new_mm_cr3(); (1) (ret=0)
<idle>-0 [012] d.... 361.071508: funcgraph_entry: 0.251 us | switch_ldt(); (1) (ret=0)
<idle>-0 [012] d.... 361.071508: funcgraph_exit: 5.901 us | } /* switch_mm_irqs_off */ (0) (ret=0)
Each function's return value will be printed at the function's return point.
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